1. Field of Disclosure
The present disclosure relates to the field of wind energy conversion. More specifically, the present disclosure relates to an induced-flow wind power system that engages and converts both potential and kinetic wind energies to effective airflow power, delivering induced (accelerated) airflow in a controlled flow field to a turbine and, as a result, extracting (converting) more than 80% of the combined effective wind power to mechanical power.
The induced-flow wind power system can be mechanically coupled with an electrical generator to produce electrical power (AC and/or DC), or mechanically coupled with a compressor to (i) pump ambient air into a high-pressure energy storage vessel (example: air-supported structure or a container) for subsequent controlled expulsion of the compressed air through a high velocity jet to a secondary turbine/rotor, coupled with an electrical generator, to effectively produce consistent electrical power output, and (ii) to pump air to a pressurized structure, such as an air-supported structure, to ensure its structural integrity.
2. Description of Related Art
Two main categories of wind power conversion systems are referenced herein (i) conventional wind turbine, and (ii) novel Venturi-type airflow delivery concepts. Specifically, conventional wind turbines are in their mature technology stage and are classified as Vertical Axis Wind Turbines (VAWT), which are primarily associated with wind-mechanical-electrical power conversion efficiencies between 25-30% and the Horizontal Axis Wind Turbines (HAWT), which leads the conventional category in efficiency of 35-47% extraction of the open flow wind power. Both types of conventional wind energy systems rely on and convert, within their respective efficiencies, the open flow wind power (input wind energy) which directly engages the turbine/rotor swept area.
Novel Venturi-type airflow delivery concepts are in their early stage of technological development. These concepts are generally ducted systems, which also use conventional type turbines/rotors interposed within the constricting ducted flow field where airflow power is harnessed and converted to mechanical-electric power. As in any conventional wind power system, novel Venturi-type concepts also rely on the input (kinetic) wind power from the open flow wind for mechanical-electrical power generation. These systems harness the open wind at the intake section (swept area) of the duct and further directs the flow through a constricting area to the turbine. Subsequently, the intake area of the duct has a larger diameter (swept area), which for the sake of comparing efficiencies should be comparable to the swept area of a conventional system, and the throat area with a relatively smaller diameter, wherein a smaller diameter (smaller swept area) conventional type turbine/rotor may be interposed.
The novel Venturi-type airflow delivery concepts suggest, that by harnessing the open flow wind through a larger intake and diverting the wind (airflow) through a constriction to the turbine will result in an accelerated wind (airflow) stream, per a Venturi-effect, and subsequently result in a higher airflow power density, which is then harnessed by the turbine.
However, as described herein, both conventional and novel Venturi-type airflow delivery concepts rely on the kinetic (push) energy of the wind, i.e., the Wind Power Density expressed in watts per meter squared of the swept area (W/m2). Subsequently, the total effective power that can be produced by any wind energy conversion system is proportional to the open flow wind (airflow) power density, as a function of the air density and the cube of wind velocity, multiplied by the effective swept area (the area engaged by the open flow wind) and reduced by friction losses and imperfection in turbine/rotor design.
Furthermore, Betz's law indicates that the theoretical maximum power that can be extracted from the wind in open flow, independent of the design of the wind turbine, is 16/27 (59.3%) of the kinetic (push) energy. Therefore, the technological drivers in wind energy conversion aim to extract wind power closer to Betz's limit.
As it is known, the five main directions of R&D in today's wind industry aim to convert the push force related to the kinetic energy of the wind to mechanical-electrical power. These efforts include:                1. Increase the intake wind power density to the turbine;                    Geographical locations (off-shore wind, wind valleys, elevated points, etc.) and            Wind in-take channels (Venturi) for accelerating wind to the turbine                        2. Increase rotor swept area (develop and introduce new, stronger and lighter materials to provide stability);        3. Increase effectiveness of the wind energy conversion (aerodynamics of the blades, fans, and rotors);        4. Increase power generating capabilities and effectiveness (permanent magnet generators (PMG)); and        5. Reduce the unpredictability effect of the wind (energy storage systems).        
Within the sphere of the technical advancements to date, HAWT are still the most advanced in terms of their ability to extract more of the available wind energy for any given swept area. This is because HAWT use most of its turbine/rotor diameter to harness the open wind flow. The VAWT, by its design, only harnesses wind power with ⅓ of its total rotor area at any point in time, giving VAWT an automatic disadvantage, compared with HAWT, in terms of the maximum attainable efficiency relative to the available open flow wind power.
Novel Venturi-type systems, harness open flow wind at the system's largest intake point (swept area) and redirect the wind flow through a constriction to increase the wind (airflow) velocity and the overall wind (airflow) power density (W/m2) that is delivered to a generally smaller diameter turbine/rotor, which is interposed in the constriction section of the ducted flow field. Although the airflow velocity may be increased through this process, the total available open flow wind energy, swept by the intake of the duct, doesn't increase. Furthermore, ducting and diverting the airflow causes partial energy loss due to friction, which adversely affects the extraction (conversion) efficiency of the open flow wind power to mechanical-electric power in such systems.
Respectively, according to the Energy Conservation law, just increasing the velocity of the wind flow in the constricting flow field does not increase the overall wind power that is made available in the flow field for extraction (conversion) to mechanical-electric power, which is a function of the harnessed open flow wind power density and the intake/swept area. Consequently, ducting the open flow wind through a constriction, in order to accelerate the velocity of the airflow to the turbine, adversely affects efficiency, compared with HAWT, due to friction losses, resulting in less overall wind power that is available in the ducted flow field for subsequent extraction (conversion) by the smaller swept area turbine; relative to the total available open flow wind energy that's is harnessed by the larger intake section at the front-end of the flow field, which is ultimately the area and the total available wind power reference that should be used in comparing extraction (conversion) efficiencies of any wind power system, specifically in comparing advantages of conventional and novel wind power technologies.
3. Advantages of the Invention
According to the Energy Conservation Law, any energy conversion system can extract only a fraction of the total available energy. The total available energy for conventional wind power systems and novel Venturi-type airflow delivery systems is the kinetic energy of the open flow wind that engages the effective swept/intake area of the system. The total available energy for the induced-flow wind power system is comprised of (i) the kinetic energy of the open flow wind engaging the active-flow nozzle intake (35%), (ii) the potential energy of the open flow wind engaging the passive-flow nozzle intake (55%), and (iii) the potential energy of the ambient wind overpassing the aerodynamic airfoil configuration 10%. Therefore, the main advantage of the induced-flow wind power system is that it accesses more available energy for extraction (conversion) than the former conventional and Venturi-type systems.
The combined effective power extraction (conversion) efficiency of the induce-flow wind power system can be measured against HAWT efficiencies with comparable swept areas and open flow wind conditions, providing a relative 160% advantage for the Induced-Flow Wind Power System over the highest rated efficiencies attained by HAWT.
The induced-flow wind permits the incorporation of a higher efficiency industrial type radial-to axial airflow turbine/rotor, such as a Francis-type turbine modified configuration, which can (i) more effectively convert the combined wind energy to mechanical-electrical power with 80% efficiency, and (ii) acting as a flywheel, stabilize energy production during wind gusts.
Furthermore, the absence of moving components at higher elevation reduces the dynamic pressure that is applied to the system, which provides an advantage for operation in higher velocity wind conditions. Specifically, permitting induced-flow wind power system to operate within a wider range of ambient wind conditions, harnessing closer to 100% of the Betz limit in accordance with a wind distribution curve for any geographic location, while a conventional wind power system will harness closer to 75% to 80% of the Betz limit in the same geographic location. This advantage is further amplified through a synergetic coupling of the induced-flow wind power system with a high-pressure energy storage vessel, such as an air-supported structure, through a compressor, which allows the system to pump ambient air to the pressurized structure in any wind condition for energy storage and subsequent controllable distribution to a secondary turbine/rotor coupled with an electrical generator; thereby, producing consistent power output and eradicating the unpredictability effect in wind power generation.